1. Field of the Invention
This invention relates to a laser beam processing method for a wafer for processing a wafer such as a semiconductor wafer or an optical device wafer using a laser beam.
2. Description of the Related Art
A wafer such as a silicon wafer or a sapphire wafer which has a plurality of devices such as ICs, LSIs, LEDs or the like formed on the surface thereof such that the devices are partitioned by division lines is divided into individual devices by a processing apparatus, and the divided devices are utilized widely in various electric apparatus such as portable telephone sets or personal computers. For the dividing of a wafer, a dicing method in which a cutting device called dicer is used is adopted widely. In the dicing method, a cutting blade of approximately 30 μm thick formed by binding abrasive grain of diamond or the like with metal or resin is rotated at a speed as high as approximately 30,000 rpm to cut into a wafer to cut the wafer into individual devices.
Meanwhile, in recent years, a method has been proposed wherein a pulse laser beam of a wavelength having absorbability by a wafer is irradiated upon a wafer to form laser processed grooves (dividing grooves) and then external force is applied using a breaking apparatus along the laser processed grooves to cut the wafer into individual devices (refer to, for example, Japanese Patent Laid-Open No. Hei 10-305420). Formation of laser processed grooves by a laser processing apparatus can raise the processing speed in comparison with a dicing method by a dicer and can process even a wafer made of a material of high hardness such as sapphire or SiC comparatively easily. Further, since the width of processing grooves can be set to a small width of, for example, less than 10 μm, the number of devices to be taken per one wafer can be increased in comparison with an alternative case wherein a dicing method is used for processing.
In processing of a wafer by a laser processing apparatus, a wafer is adhered to a dicing tape adhered at an outer peripheral portion thereof to an annular frame such that the wafer is supported on the annular frame through the dicing tape. Then, a laser beam is irradiated in a state in which the wafer is sucked to and held by a chuck table of the laser processing apparatus through the dicing tape.